It has previously been proposed to provide air-bag inflators which incorporate one or two bottles of pressure vessels containing gas under pressure. Each bottle is initially sealed, for instance by a metal foil. The foil can be initially supported by means of a support element which is held in position against the exterior side of the foil. When the inflator is triggered the support element is moved away from the metal foil, enabling the foil to rupture under the pressure of the gas within the bottle, and enabling the gas to escape from the bottle and flow into the interior of the air-bag to inflate the air-bag.
In known inflators of this type one bottle may contain a fuel, in the form of an oxidisable gas, and another bottle may contain an oxidising gas. When these gases escape from the gas bottles they are mixed, and may subsequently be ignited within the air-bag to complete inflation of the air-bag. As an alternative only one bottle can be used, containing suitable reactive or non-reactive gases.
EP1778526 and U.S. Pat. No. 6,612,326 disclose arrangements of this type in which a support element is initially provided immediately behind a foil, and held in position by a flange of a piston head, or by a support that is arranged to be knocked out of position by a piston head. When the air-bag is to be triggered, the piston is driven so that the flange or support moves away from the region behind the support element, thus allowing the support element to move away from the foil, and so allowing the pressure of gas within the bottle to rupture the foil, pushing the support element away as this occurs.
In order for systems of this type to be effective, the foil must be relatively thin, and the pressure of gas within the bottle must be relatively high. If the foil is too thick, or the pressure of gas within the bottle is too low, there is a risk that the foil will bulge elastically and will not rupture at the required time, particularly in low-temperature conditions.
Other known systems do not include a movable support, and instead utilise an arrangement for actively piercing the foil. However, these systems inevitably involve additional moving parts, increasing the cost, complexity and likelihood of failure.